Filter paper form analysis sheets or multilayered analysis sheets are known as useful material for rapid, simple, dry process semi-quantitative or quantitative analysis of specific chemical components contained in an aqueous liquid such as body fluid (e.g., blood, serum, urine or spinal fluid). Multilayered analysis sheets are described in detail in, for example, Japanese patent application (OPI) No. 53888/74 (U.S. Pat. No. 3,992,158), U.S. Pat. No. 3,992,158, Japanese patent application (OPI) Nos. 137192/75 (U.S. Pat. No. 3,983,005), 40191/76 (U.S. Pat. No. 4,042,335), 3488/77 (U.S. Pat. No. Re. 30,267), 131786/77 (U.S. Pat. No. 4,050,898), 131089/78 (U.S. Pat. No. 4,144,306), 29700/79 (U.S. Pat. No. 4,166,093), 34298/79 (U.S. patent application Ser. No. 814,770, filed July 11, 1977), 90859/80 (U.S. Pat. No. 4,258,001), U.S. Pat. Nos. 4,110,079, 4,132,528 (the term "OPI" as used herein refers to a "published unexamined Japanese patent application"), and Clinical Chemistry, Vol. 24, pp. 1335-1350 (1978), etc. Such multilayered analysis sheets are comprised of a support having previously laminated thereon a liquid sample-spreading layer and a reagent layer containing reagents necessary for the intended analysis. In practicing chemical analysis, quantitative analysis can only be conducted by two fundamental procedures of applying a drop of test sample onto the sheet and measuring color change in terms of optical denesity. Thus, they are dry-process chemical analysis materials which do not require use of test tubes, preparation, weighing and addition of reagent solutions, and strict weighing-out of samples; as distinct from conventional analytical methods.
The fundamental structure of such multilayered chemical analysis sheet includes a support, a reagent layer, and a sample-spreading layer in that order. The reagent layer is formed by incorporating a reagent in a binder, such as gelatin, and forming it into a thin layer. The reagent layer may be a single layer, separated into different layers such as a first reagent layer and a second reagent layer, or may contain additional layers such as detection layers, or dye-receiving layers. In addition, an interlayer called a color- (radiation-) blocking layer or a barrier layer may be provided between the spreading layer and the reagent layer or between a plurality of reagent layers. The sample-spreading layer is provided as an outermost layer of the analysis sheet, to which a liquid sample is to be applied. The sample-spreading layer functions to transport the liquid sample in an almost definite quantity per unit area to the reagent layer regardless the volume of the applied liquid sample, i.e., functions to substantially uniformly spread the sample.
The liquid sample-spreading layer as described above is decribed in detail in the aforesaid patent specifications and literature. These descriptions indicate that non-fibrous porous media are effective as such sample-spreading layer.
Examples of such non-fibrous porous media include brush polymer (general name: membrane filter) and a dispersion of a porous material such as diatomaceous earth or a fine crystalline material (e.g., fine crystalline cellulose (trade name: Avicel, made by FMC Corp.), etc.) in a binder, porous joining material made by point-to-point adhesion of glass or resin fine spherical beads (see U.S. Pat. No. 4,258,001). The non-fibrous porous media illustrated must contain voids uniformly positioned in every direction or have an isotropic porosity as clearly described in U.S. Pat. No. 3,992,158.
Japanese patent application (OPI) Nos. 53888/74 and 90859/80 and U.S. Pat. No. 3,992,158 disclose in detail the process for forming the liquid sample-spreading layer composed of a non-fibrous, isotropically porous medium. However, a known sample-spreading layer composed of a non-fibrous porous medium is undesirable because when a sample applied to it contains protein in a high concentration (e.g., blood serum), the ability of the layer to spread the applied liquid sample varies substantially depending upon the content of the protein. Accordingly, the quantitative aspect of the analysis is spoiled.
When the non-fibrous porous medium is a structure comprising self-adhesive particles, heat- or solvent-softened particles are liable to readily fix and fill voids within the structure. Accordingly, many high molecular weight materials present in an aqueous liquid sample to be analyzed result in readily stuffing and therefore inhibit the fluid flow within the structure. When the structure is composed of particles bound to each other through an adhesive, stuffing also can take place due to the volume of the adhesive, thus inhibiting the flow of a fluid containing composite high molecular weight materials.
Therefore, multilayered chemical analysis materials containing such non-fibrous porous medium as a liquid sample-spreading layer are not suited for analysis of body fluid containing macro-molecules or whole blood containing erythrocytes.
One approach for removing the defects described above with known non-fibrous porous medium-containing liquid sample-spreading layer is described in Japanese patent application (OPI) No. 90859/80. The present inventors have formerly proposed to use fabric rendered hydrophilic as a liquid sample-spreading layer for a multilayered chemical analysis material (U.S. Pat. No. 4,292,272) as an art absolutely different from that disclosed in Japanese patent application (OPI) No. 90859/80. The spreading layer using such a fabric rendered hydrophilic removes defects of known non-fibrous porous media with respect to ease and stability of production steps, production cost, and sample-spreading properties.
The multilayered chemical analysis sheet having a spreading layer of fabric rendered hydrophilic is excellent to enable one to use the whole blood upon quantitative analysis of blood component. However, it still has several problems.
When preparing a spreading layer from natural fiber such as 100% cotton, it is difficult to attain uniform spreading of an applied liquid sample as compared to a fabric containing a chemical or synthetic fiber due to non-uniformity in the yarn structure, particularly in disposition or weaving manner of twisted yarns. Furthermore, a spreading layer composed of natural fiber alone is difficult to handle due to its strong water-absorbing properties, generally high water content, and high stretchability. In addition, with respect to the whole blood-spreading properties, the layer composed of a natural fiber is inferior to that composed of a fabric containing a chemical or synthetic fiber. On the other hand, a sample-spreading layer composed of a fabric containing a chemical or synthetic fiber makes it possible to attain uniform spreading of an applied liquid sample due to uniformity in yarn structure, particularly in disposition and weaving manner of twisted yarns. A chemical or synthetic fiber is easy to handle due to weak or substantially no water-absorbing properties and small stretchability. Further, such a spreading layer composed of a fabric containing a chemical or synthetic fiber has an excellent whole blood-spreading ability. However, it has such poor adhesiveness that it is easily delaminated when subjected to cutting or punching work.
As a result of intensive investigations to remove the defects with such spreading layers composed of fabrics containing chemical or synthetic fibers, the inventors have achieved the present invention.